The present invention relates to a high frequency semiconductor integrated circuit which is used in mobile communication equipment such as a portable telephone.
Owing to recent advancement of the mobile communication technologies, there have been demands for high frequency semiconductor switches and high frequency semiconductor variable attenuators, which are small in size and require a low power consumption. These switches and attenuators are used for switching a communication mode (transmission and receipt mode) of an antenna of a portable telephone or the like and controlling an input level of a power amplifier. As a device used in such switches and attenuators, there has been used a basic circuit shown in FIG. 8 which includes a field-effect transistor (FET).
In FIG. 8, a reference number "1" indicates a normally-on field-effect transistor, which is formed at a portion of a Ga-As substrate (not shown) and includes a gate, a source and a drain. A reference number "3" indicates a control terminal. Reference numbers "6" and "7" indicate first and second signal terminals, respectively. In this structure, a control voltage signal is applied to the gate of the field-effect transistor 1 via the control terminal 3 and the value of the voltage control signal is changed, whereby a quantity of high frequency signals transmitted between the first and second signal terminals 6 and 7 are controlled.
FIG. 9 shows a circuit structure including two basic circuits, each of which is the same as that shown in FIG. 8. In each of the basic circuits, the first signal terminal 6 is connected to a common input terminal 10. In one of the basic circuits, the second signal terminal 7 is used as an output terminal. In the other basic circuit, the second signal terminal 7 is connected to a ground terminal. In this circuit, complementary control signals are supplied to the control terminals 3 of the respective basic circuits so that the quantities of signals transmitted in respective basic circuits are controlled complementarily. Thus, when the field-effect transistor is off in the basic circuit transmitting high frequency signals to the output terminal, high frequency signals are sent to the ground terminal, so that significantly excellent isolation can be achieved.
However, the circuit shown in FIG. 9 including combination of the conventional basic circuits suffers from the following problems.
As already describe with reference to FIG. 9, a high frequency control circuit such as a switch includes a basic circuit shown in FIG. 8 as a unit, and also includes another basic circuit interposed between the input and the output, between the input and the ground, or between the output and the ground of the former basic circuit. This structure requires two control terminal systems for receiving complementary control voltage signals. The circuit shown in FIG. 9, for example, requires two control circuits for supplying complementary control voltage signals to the respective control terminals 3 of the basic circuits. Thus, two control terminals are essentially required, and further a complicated structure is required in a peripheral circuit for driving the high frequency control circuit. A similar problem also arises in a bridge T-type attenuator including combination of unit circuits, each of which is the same as that shown in FIG. 8, because it requires two control systems for inputting two complementary control signals, although this is not discussed.
Furthermore, such a problem may arise that linearity characteristics between the input and the output deteriorates, and thus distortion in the output is increased, when a high frequency signal of a high power is inputted. Therefore, when the basic circuit shown in FIGS. 8 and/or those shown in FIG. 9 are used in combination as a switch or an attenuator, only a restricted power can be applied.